1. Field of the Invention
The present invention relates to load measuring sensor gauges for measuring loads, as well as to load measuring systems using such sensor gauges. More particularly, the present invention relates to sensor gauges and systems, wherein load is applied to an elastically deformable structure to produce an elastic deformation in the structure. The applied load is then measured using an induced-voltage sensor gauge configured to detect an induced voltage corresponding to the produced elastic deformation.
2. Background of the Related Art
Typically, general-purpose electronic scales, industrial electronic scales and the like utilize so-called “electric resistance type load cells”. Such load cells employ a strain gauge using resistive wire. In such load cells, when a strain is experienced by a structure due to application of load, the strain is detected as a change in electrical resistance of the resistive wire, and is then converted into an electrical signal that in-turn is measured, thereby enabling measurement of the applied load.
Currently, load cells with strain accuracy as high as between about 1/3,000 and 1/5,000 are generally available. It is very difficult to implement a load cell with accuracy higher than the above accuracy. This is because there are problems in that typically a layer of adhesive is used to attach a strain gauge to its supporting structure, and the adhesive can distort. Thus, strain produced in the structure is transferred, but extension and compression behavior of the structure is modified. Further, because the adhesive is made of polymer that has an inhomogeneous amorphous structure, the adhesive exhibits non-uniform mechanical properties that cannot be easily predicted.
Inherent features of typical strain gauges also adversely affect attaining higher accuracies. Particularly, a back plate which is typically made of a polymeric material such as phenol or polyamide, and which is placed below the resistive material of the strain gauge, inhibits the transfer of strain.
Further, because it is difficult to achieve a uniform profile of the resistive material throughout the strain gauge, it is also difficult to obtain uniform deformation thereof that is proportional to a compressive or tensile strain of a structure.
Another prior technique for measuring load uses an electromagnetic force balancing type load measuring transducer. However, since this load measuring transducer employs a very complicated mechanical mechanism, the load measuring transducer is difficult to manufacture and is very expensive. In addition, there are electrical and spatial limitations on increases of electromagnetic force, serving as balancing forces for applied loads. Further, since the complicated mechanical mechanism includes many thin hinges, there are problems in that it is not suitable for measurement of heavy loads and it is very vulnerable to external impacts.
Due to the above problems, such a load measuring transducer cannot easily be used in general-purpose commercial electronic scales or industrial electronic scales and only selectively used in special-purpose electronic scales.
To solve the above problems, related technologies are disclosed in Korean Patent Registration No. 10-0500736 and U.S. Pat. No. 7,258,028 B2.
In the prior art, when eccentricity is produced in a gauge due to applied load, measurement errors occur in the gauge. In order to prevent this problem, the patterns of a stationary coil and a moveable coil are formed on a concentric arc shape, thereby easily accommodating the eccentric phenomenon that occurs when a load is applied.
However, this method is not a fundamental solution for preventing errors caused by eccentricity. Accordingly, there is a need for a method of fundamentally solving the such eccentricity problems.
In the referenced prior art, two gauges, each having electric wire patterns repeatedly formed thereon, are arranged facing one another, and an Alternating Current (AC) voltage applied to one of the gauges induces an AC voltage in the other of the gauges, which is measured, which corresponds to the applied load. An example shape for such gauges is shown in FIG. 6.
However, the above-described prior art suffers from problems relating to the short, connecting wired, which are perpendicular to the longer wires, adversely influence the overall magnetic field, resulting in errors. This is because an induced voltage is determined by relative positions between long, parallel electric wires. In order to solve these problems, the amount of voltage generated by the short electric wires must be theoretically calculated and corrected.